I just did this to my van. Since I installed a CD heater and use it overnight boondocking I'm sensitive to every watt used by my one house battery.
The big penthouse lights = ~35 watts each including the ballast. After LED retrofit now about 5 watts each.
I bought from https://www.superbrightleds.com/
RLBN-NW30SMD: Natural White $7.95
C21-I06: Interconnect-6 Inch Long $0.45
C21-I18: Interconnect-18 Inch Long $0.90
MCBRF-4A: Mini Single Color LED Controller $9.95
I cut the interconnects in half and used them as power connections too.
These made the job WAY simpler, NO soldering!
Solder Seal Wire Connectors, Heat Shrink
Use a dimmer, totally worth it!
Cut the LED strips to fit. The left over pieces can be used elsewhere.
Keep track of the polarity! Otherwise you'll be switching and reconnecting the power to fix.
I left all the fluorescent light stuff in place cause I'm lazy and incase I wanted to go back. There's enough room to work around it.
But I'm not switching back. The LEDs and remote controlled dimmer work WAY better.